I am grinding completion for gold and I love to go purist with every new class to see if I can beat all the dungeons that way. I take Bet on Boss because the gold grind is already heinous as it is... and I feel a bit slighted losing Purist badge on something that in no way benefits the run.

I'd agree that Bet on the Boss shouldn't disqualify you from purist, especially since badges only offer a one-time gold bonus anyways. If badges offered repeatable gold bonuses (I personally think they should) that might be another matter, but they don't so I really don't see the harm.

I've been suggesting this just about any time I was suggesting anything... It has actually "screwed" me out of a purist badge many times as I used to prep it automatically and foget that I had it prepped as my brain didn't register it as a prep. XD

Bet on Boss is a strange prep. It effectively slaps a big opportunity cost in gold on all the other Thief Den preps, making them effectively the most expensive preps by far. (This is assuming you can win in a small number of attempts, of course, but then if you need a lot of prepped attempts to solve a dungeon, you're not in it for the money any more.) I'm not sure it really needs to be in the game at all, since it doesn't really add much to the decision-making process before a run.

^ I was at one point suggesting that there be several mutualy exclusive "tokens" simmilar to the vicious token, with bet on boss as one of them. As easily identifiable preps which don't affect purist (and so you couldn't stack VT and bet on boss). However, everyone would be prepping it on almost every run then, I suppose, which kinda just makes the boss throphy worth more. Still, most people prep it allmost all the time anyway, and it's such an anomalous prep that even after the previous sentence, solid ground to dismiss the idea, I still don't know...